The present invention concerns a method for welding the far ends of elongated elements together, such as pipes, rails, rods, iron sections, etc. by means of friction welding, whereby the above-mentioned far ends are heated up to forging temperature by rotating a ring clamped in between them.
In order to weld such elongated elements, the same techniques as for welding plates have long been used, namely techniques whereby filamentary material is added to the weld.
Not only are such welds very difficult to apply for the welder, as he has to weld in very awkward positions, but there may also arise faults and distortions in the welds, which results in risks of leaks or cracks, especially in the case of pipelines.
That is why it is already known for pipelines to connect the far ends of the elements by means of friction welding.
In the case of friction welding, the elements to be welded are rotated about their axes, one in relation to the other, while these elements are pushed one against the other, so that the elements situated next to one another heat up thanks to the friction and melt together.
As only the surfaces to be welded are heated, this is a very efficient technique, but ordinary friction welding cannot be applied in case of long elements such as the pipes of a pipeline, since these elements cannot be rotated about their axes in practice.
However, in order to apply friction welding, use is made of a ring in the case of pipelines which is put in between two pipes to be welded together, and it is rotated until the ring and the far ends of the pipes reach the forging temperature.
In such a known method, use is made of a conical ring which is rotated and upon which is exerted a radial pressure, while the pipes are being held tight.
The shape of the far ends of the pipes is complementary to the conical ring.
As the force with which the ring is radially pushed against the far ends of the pipes is usually not sufficiently large, the quality of the weld is of ten bad.
DATABASE WPI Section Ch, Week 197921 Derwent Publications Ltd., London, GB; Class M23, AN 1979-40161B XP002131895 discloses a method for welding the extremities of two elongated elements together by means of friction, whereby the above-mentioned extremities are heated up to forging temperature by rotating a ring clamped in between them by means of hydrocilinders. As soon as the forging temperature is reached, the pressure is increased and the elements are pushed towards one another with a great force.
The invention aims to remedy the above-mentioned and other disadvantages, and to of for a method far welding elongated elements whereby a weld of excellent quality is obtained.
This aim is reached according to the invention by a method for welding the ends of two elongated elements together by means of friction welding, whereby the above-mentioned ends are heated up to forging temperature by rotating a ring clamped in between them, and, as soon as the forging temperature is reached, the elements are pushed towards one another with great force, which method is characterised in that a flat ring is provided between the ends, the elements are axially drawn towards each other and these elements are pushed towards one another with great force by at least one stroke exerting at least once a sudden axial dynamic force.
This exertion of a dynamic force may consist of one or several pneumatic hammer strokes, but it can also be obtained by means of an explosion.
Preferably, the elongated elements are entirely drawn towards one another in their longitudinal direction.
The invention also concerns a device which is particularly suitable for applying the above-described method.
Consequently, the invention also concerns a device for welding two elongated elements together, by means of friction welding according to the above-mentioned method, whereby this device contains driving means to rotate a ring, drawing means to draw the elongated elements together, and means to exert axially a stroke or sudden dynamic force, preferably consisting of an explosion room or a mechanical hammer.